1. Field of the Invention
The present invention relates to a gear shifting control system of a continuously-variable transmission, and more particularly, to suppression of variation in an output shaft torque occurring during gear shifting.
2. Description of Related Art
In order to suppress a variation of an output shift torque occurring when an inertia phase is started in so-called upshifting which is gear shifting to a speedup side of an automatic transmission, a gear shifting controller of an automatic transmission is known which performs a so-called torque-down control of decreasing an engine torque during gear shifting by controlling an electronic throttle valve of an engine so as to decrease a throttle opening. An example of the gear shifting controller of an automatic transmission is described in Japanese Patent Application Publication No. 3-157560 (JP 3-157560 A).
JP 3-157560 A describes that a region (hereinafter, referred to as dead zone) in which the variation of the engine torque with respect to the variation of the throttle opening is small is present in a high-opening region of the electronic throttle valve. In this regard, when upshifting is carried out from the high-opening region of the electronic throttle valve, the decrease in the engine torque is delayed with respect to the decrease in the throttle opening and the torque-down control is not performed from the gear shifting start time, whereby there is a problem in that a sufficient gear shifting shock reducing effect based on the torque-down is not obtained. As a solution to this problem, JP 3-157560 A discloses a technique of enabling the start of the torque-down of the engine at the inertia phase start time of the automatic transmission by decreasing the throttle opening of the electronic throttle valve up to the lower end of the dead zone in advance before starting the inertia phase of the automatic transmission when the gear shifting of the automatic transmission is determined.